1. Field of the Invention
The present invention relates to a toner for use in a developer developing an electrostatic latent image in electrophotography, electrostatic recording and electrostatic printing, and to an electrophotographic image forming apparatus using the toner.
2. Discussion of the Background
Typically, in an electrophotographic or an electrostatic recording image forming apparatus such as copiers, printers and facsimiles, an electrostatic latent image based on an image information is formed on a latent image bearer such as photoreceptor drums and photoreceptor belts; an image developer forms a toner image by transferring a toner onto the latent image bearer; and the toner image is transferred onto a recording medium to form an image. In such a system, a residual toner on a surface of the photoreceptor needs to sufficiently be removed after a toner image is transferred because the surface thereof is repeatedly used to form the toner images. Several methods of removing the residual toner have conventionally been studied, and a method of scraping the residual toner by contacting a cleaning blade to the surface of the photoreceptor is widely in practical use because of being low-cost and capable of downsizing the whole system.
The toner removal efficiency of the above-mentioned method largely depends on a contact pressure between the photoreceptor and cleaning blade, and on a surface profile of the photoreceptor or a developing sleeve. Similarly, in terms of toner properties, the toner removal efficiency largely depends on the shape of a toner and surface profile thereof. When the toner removal is insufficient, the residual toner filming over a surface of the photoreceptor drum occurs. Further, the accumulated filming increases a stress between the photoreceptor and cleaning blade, resulting in occurrence of the toner fusion bond due to a heat generation and a fatigue abrasion of the photoreceptor. The more accelerated such problems, the smaller the particle diameter of the toner. The surface of the photoreceptor is not sufficiently cleaned because an adherence of such a toner to the photoreceptor increases and an amount of the toner scraping through a gap between the photoreceptor and cleaning blade increases.
To solve these problems, Japanese Laid-Open Patent Publication No. 2000-267331 discloses an image forming method wherein a toner has a shape factor, i.e., SF-1 of from 125 to 130, and a particle diameter of the toner and a content thereof having such a shape factor are specified; Japanese Laid-Open Patent Publication No. 2000-023408 discloses a blade brush cleaning method wherein a toner having a SF-1 of from 100 to 160 is 65% by number; Japanese Laid-Open Patent Publication No. 2000-029297 discloses a method of using a magnetic carrier having a SF-1 of from 100 to 140, a SF-2 of from 100 to 120 and a specific resistance of from 1×1010 Ω·cm to 1×1014 Ω·cm; Japanese Laid-Open Patent Publication No. 09-179411 discloses a method wherein a developing sleeve and a photoreceptor drive in the same direction at a peripheral speed ratio of from 0.5 to 1.8, and the toner has a SF-1 of from 135 to 150 and a SF-2 of from 115 to 125; and; Japanese Laid-Open Patent Publication No. 7-49585 discloses a toner having a spheric shape and an amorphous shape at a constant rate. All of these specify the shape factor of the toner to mainly improve cleanability and transferability thereof, and are not limited to an improvement of the cleanability.
However, only with such a specification of the shape factor of the toner, the surface of the photoreceptor is not occasionally cleaned well depending on the conditions of the method. Particularly, such problems occur when the toner has a smaller particle diameter or a smooth surface with less concavities and convexities, and when a contact pressure between the surface of the photoreceptor and cleaning blade in an image forming apparatus is low. The toner having a small particle diameter has a higher adherence to the photoreceptor and tends to remain thereon even after development, and therefore the cleaning members are easily consumed. Further, the residual toner contaminates a charging roller charging the photoreceptor while contacting thereto and impairs the charging capability of the charging roller. On the contrary, a toner having a large particle diameter has a good cleanability but has a poor transferability, resulting in deterioration of image resolution.
On the other hand, it is known that the cleanability of the toner largely depends on the surface nature thereof, which is largely influenced by a toner production method such as pulverization methods and polymerization methods.
A toner produced by a conventional kneading and pulverizing method has an advantage in the cleanability because of being amorphous, but it is not easy to control a shape and a surface structure of the toner. Further, it is difficult to narrow a particle diameter distribution of the toner and to make the toner have an average particle diameter not greater than 6 μm in terms of classifying capability, yield, productivity and cost. Japanese Laid-Open Patent Publication No. 11-133665 discloses a dry toner using an elongated urethane-modified polyester as a binder and having a practical sphericity of from 0.90 to 1.00. The fixability, transferability and fluidity of the toner are improved, but the cleanability thereof is lower than that of the pulverized amorphous toner.
Japanese Laid-Open Patent Publications Nos. 11-149180 and 2000-292981 disclose a spheric dry toner having a small particle diameter and an economical method of producing the toner, which has good powder fluidity, transferability, thermostable preservability, low-temperature fixability, hot offset resistance, and which produces images having good glossiness particularly when used in a full-color copier and does not need an oil application to a heat roller, wherein the dry toner includes a toner binder formed from an elongation and/or a suspension reaction of a prepolymer including an isocyanate; and a colorant, and wherein the toner is formed from the elongation and/or suspension reaction between the prepolymer and amines in an aqueous medium. However, the spheric toner does not have both good cleanability particularly with a blade cleaner and transferability yet.
The toner disclosed in Japanese Laid-Open Patent Publications Nos. 11-149180 and 2000-292981 is produced by the above-mentioned polymerization method to have a particle diameter distribution with less unevenness and a stable chargeability. The toner produced thereby has a high lubricity because of having almost uniformly less concavity and convexity and a higher sphericity than the pulverized toner. Therefore, the toner tends to scrape through a contact portion between the photoreceptor and cleaning blade and has worse cleanability than the pulverized toner. Further, the toner typically tends to have a strong adherence to the surface of a photoreceptor, and therefore has poor cleanability and produces defective images.
Because of these reasons, a need exists for a toner for developing an electrostatic latent image, which has sufficient cleanability after development and produces high-quality images.